8 Intermittent (Intelligent) Auscultation in the Low-Risk Setting. Handbook CTG

Intermittent (Intelligent) Auscultation

in the Low-Risk Setting

◈

Virginia Lowe and Abigail Archer

Handbook of CTG Interpretation: From Patterns to Physiology, ed. Edwin Chandraharan.

Published by Cambridge University Press. © Cambridge University Press 2017.

Key Facts

Intermittent auscultation (IA) is appropriate for use in the low-risk setting where

pregnancy and onset of labour have been uncomplicated. It facilitates the normal

physiology of labour by allowing freedom of movement.

The use of continuous electronic fetal monitoring in this group does not improve

neonatal outcomes, but is associated with higher rates of medical intervention.

When used cautiously, IA safely identifies the healthy fetus and promotes

normality.

Vigilance is needed in interpreting the findings to ensure signs of hypoxia or

other indicators requiring investigation are not overlooked.

This practice has been termed ‘intelligent auscultation’ to highlight the extension

beyond listening for the presence of a fetal heart, but requires an understanding

of fetal pathophysiology as well as the intrapartum hypoxic process and how this

may influence the features of the fetal heart rate (FHR).Recommended Method

On first contact, there should be a thorough review of the whole clinical picture

to ensure that pregnancy and labour have been low risk thus far. Enquiries should

be made as to when fetal movements were last noted by the mother, and this must

be documented.

The fetal heart should then be auscultated with a pinard stethoscope or hand-held

Doppler to determine the baseline rate. This is usually achieved by counting the

number of beats heard over a period of 1 minute. The heart rate is recorded as an

average number, not as a range. The choice of equipment reduces the likelihood

of mistakenly monitoring the maternal pulse, and to reduce this risk further, the

maternal pulse should also be palpated, measured and documented to

demonstrate that they are different rates.

Crucially, following this assessment, the caregiver has to establish fetal health. If

fetal movements are currently present, auscultation of the fetal heart should

reveal an acceleration of >15 beats above the baseline rate, demonstrating a

nonhypoxic fetus. If there are currently no movements (although a report that

these have previously been normal), consideration may be given to auscultation

after stimulating the fetus by palpating the maternal abdomen or following digital

scalp stimulation at vaginal examination. Again, an acceleration of at least 15

beats above the baseline should be observed.

Finally, await a contraction and auscultate the FHR for 1 minute immediately

afterwards to exclude decelerations. If there are any concerns throughout this

assessment, then CTG monitoring should be commenced. This may be

discontinued after 20 minutes if it is normal and there are no ongoing concerns

about fetal health. In a low-risk labour with normal initial assessment, the fetal

heart should be monitored for 1 minute following a contraction every 15 minutes

in the first stage and every 5 minutes in the second stage.

The baseline heart rate should be plotted on the partogram. If any decelerations

are heard, or if a rise in baseline is noted, further investigation is indicated

immediately.Physiology behind IA

Pitfalls

IA should be the method of choice, where appropriate (i.e. ‘low-risk’

pregnancy), as it allows the mother to move freely, facilitating the normal

physiology of labour. Furthermore, it avoids the use of CTGs in low-risk labour

as the use of CTG in this situation may be subject to misinterpretation, raising

the likelihood of unnecessary intervention.

Accelerations demonstrate good fetal health as a reflection of an intact somatic

nervous system (see Chapter 2). These may be associated with fetal movement

or stimulation or may be spontaneous.

Once chronic hypoxia has been excluded using the method above, then –

excluding catastrophic events – for the fetus to become hypoxic, it will display

decelerations and then a gradually rising baseline. This will be detected when

following the principles of IA and a more intensive assessment of fetal health

must be initiated.

Quiet and active epochs (‘cycling’) are evidence of an intact central nervous

system and will be apparent on the partogram.

Evidence suggests that the type of deceleration cannot be established by using

IA. By auscultating the fetal heart after a contraction, any decelerations heard

will warrant further investigation. These will either be variable (cord

compression) or late (utero-placental insufficiency/chemoreceptor stimulation)

and will not have recovered by the time the contraction has passed.

Decelerations that occur exclusively during contractions are not usually

associated with poor neonatal outcomes.

FHR changes unrelated to hypoxia may also be detected. An evolving

tachycardia driven by infection, maternal pyrexia or dehydration will be visible

on the partogram. Again, immediate assessment is required, including CTG

analysis.A thorough initial assessment is needed to exclude any conditions that may

increase the likelihood of hypoxia developing in the fetus. IA is not appropriate

in these cases.

FHR must always be recorded as a single average figure, not a range. This

allows trends to be seen clearly on the partogram.

The fetal heart must be auscultated immediately following a contraction. Any

delay may mean that the window of opportunity to hear decelerations may be

missed, therefore failing to identify the first evidence of hypoxia.

Baseline rate and the presence of accelerations and decelerations can be

correctly identified using IA. There is, however, no evidence that either types of

deceleration or variability can be identified. This is not a weakness of IA: the

parameters necessary to highlight the fetus requiring further assessment can be

detected. If the caregiver is attempting to monitor variability through IA, they

have misinterpreted the principles of physiology-based interpretation.

Accelerations after a contraction are physiologically unlikely, especially as

labour progresses, and are more likely to be an ‘overshoot’ following a

deceleration (Figure 8.1) requiring further investigation. This is because

‘overshoots’ denote an exaggerated fetal compensatory response to fetal

hypotension secondary to sustained compression of the umbilical cord.

A rising baseline heart rate warrants a thorough exploration of possible causes,

regardless of whether this is an absolute or relative tachycardia (consider

gradually evolving hypoxia where decelerations may not have been heard with

IA or inflammatory/infective processes).

Monitoring in the second stage of labour is more frequent due to the increasing

stressors present. However, great care must be taken to ensure monitoring is

accurate; descent of the fetal head means that the likelihood of mistakenly

locating blood flow in the maternal iliac vessels is increased. Active second

stage is also a time when maternal heart rate (MHR) is often increased due to

exertion; so misinterpretation is possible and caregivers must remain vigilant.Figure 8.1 FHR ‘overshoots’, which will be noted as repeated ‘accelerations’ after each

uterine contraction (arrows) during IA. Continuous electronic FHR recording should be

itiated to exclude ongoing atypical variable decelerations suggestive of repeated and

sustained compression of the umbilical cord.

Exercises

1. A 30-year-old primigravida presented with spontaneous labour at 39 weeks,

having had a low-risk pregnancy. On vaginal examination, cervix was 6 cm dilated,

fully effaced with the presenting part 2 to the ischial spines. Bulging membranes

were felt. She is requesting entonox for analgesia.

a. Is CTG monitoring indicated? Why?

b. On auscultation of the fetal heart, for 1 minute after the contraction, the heart

rate is heard at an average of 140 bpm. Using the principles of IA, what is your

diagnosis? What other information do you need?

c. What is your action plan following assessment?

d. Before the next vaginal examination was due, decelerations were heard using

a hand-held Doppler following a contraction. What would your actions be?

2. Having had a low-risk pregnancy, with normal scans, a 25-year-old

primigravida presented with spontaneous labour at 41 weeks and 2 days.Spontaneous rupture of membranes was confirmed on speculum 14 hours ago. On

vaginal examination, cervix was found to be 5 cm dilated, fully effaced, and well

applied to the fetal head, with the presenting part 2 to the ischial spines. Clear

liquor is noted.

a. On auscultation of FHR for 1 minute after a contraction, the fetal heart is

heard at a rate of 150 bpm. What other information do you need?

b. What are the possible causes of the findings?

c. Is CTG monitoring indicated? Why?

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